1. Field of the Invention
The present invention relates to a magnetic disk device such as a floppy disk drive (FDD) device for example, and more specifically to a magnetic head device equipped with a magnetic head for preventing any crosstalk from being caused, said magnetic head having a plurality of coils which form a corresponding plurality of provided corresponding gaps.
2. Description of the Prior Art
FIGS. 5 and 6 are side and front views illustrating a prior art magnetic head of the tunnel erasing type. In the same figures, numeral (1) designates an L-shaped read/write core which has a slidable surface (1a), (2) designates a first center core which has a slidable surface (2a) coincident with the slidable surface (1a) of the read/write core and forms a read/write gap (3), having a predetermined length, at the center of a junction between the slidable surfaces (1a), (2a). Numeral (4) designates a non-magnetic glass filler which specifies the length of the read/write gap (3) and joins the read core (1) with the first center core (2), and numeral (5) designates a first back bar connected to both ends of the read/write core (1) and the first center core (2) for forming a magnetic circuit closed by both cores (1), (2). Numeral (6) designates a read/write coil wound around the read/write core (1) and having input and output terminals (6a), (6b) for signals. Numeral (7) designates an L-shaped erasing core having a slidable surface (7a), and (8) designates a second center core having a slidable surface (8a) coincident with the slidable surface (7a) of the L-shaped erasing core and further having an erasing gap (9) formed between opposite ends of a connection portion between the slidable surfaces (7a) and (8a), in which a distance between the erasing gaps (9), (9) is slightly less than the length of the read/write gap (3). Numeral (10) is a non-magnetic filler for defining the length of the erasing gap (9), said non-magnetic filler comprises a glass agent for joining the erasing core (7) and the second center core (8). Numeral (11) is a second back bar connected to both ends of the erasing core (7) and the second center core (8) to form a magnetic circuit closed by both cores (7), (8). Numeral (12) is an erasing coil wound around the erasing core (7) and having input and output terminals (12a), (12b) through which a predetermined current is permitted to flow upon recording a signal. Numeral (13) is a non-magnetic center separator connected between the back surfaces of the first and second center cores (2), (8) and between the first and second back bars (5), (11).
The operation of the prior art magnetic head constructed as such will now be described where data is recorded and regenerated on a magnetic medium such as a floppy disk and the like. Recording of data on a recording medium will first be described. A signal corresponding to data to be recorded is applied to the input and output terminals (6a), (6b) of the read/write coil (6), and predetermined voltage is applied to the input and output terminals (12a), (12b) of the erasing coil (12). The read/write gap (3) slides on the recording surface of the recording medium ahead of the erasing gap (9). Accordingly, as illustrated in FIG. 7, a current flowing through the read/write coil (6) based upon the signal causes a magnetic field to appear in the read/write gap (3) which in turn overwrites new data on previous data (14) on the recording medium. Thus, data (15a) corresponding to the aforementioned signal is written on the recording medium. Additionally, a predetermined current has been driven to flow through the erasing coil (12), so that a predetermined magnetic flux correspondingly appears in the erasing gap (9) to erase opposite end data of the new data (15a) recorded by the read/write gap (3) and hence allow write data (15) with guard bands (16) at the opposite ends to be written on the recording medium. Alternately, when the write data (15) is regenerated (read), once the magnetic head is forced to slide on the recording surface of the recording medium without permitting a current to flow to the erasing coil (12), a magnetic flux change appears over the read/write gap (3) in response to the write data (15) to permit a current to flow through the read/write coil (6). Thus, regenerated output voltage appears at the input and output terminals (6a), (6b) of the read/write coil (6) for its regeneration.
Additionally, a magnetic head of a preceding erasing type different from the above tunneling erasing type in the conventional example 1 is also described in Japanese Patent Laid-Open No. 61-39910 for example. Referring to FIGS. 8 and 9, the magnetic head of the preceding erasing type is illustrated as a conventional example 2. The present example is different from the conventional example 1 chiefly in view of the fact that a position where the erasing gap (9) in the example 2 is formed as different from the example 1 between the both examples. Namely, the erasing gap (9) is formed at the center of a junction between the slidable surfaces (7a), (8a) of the erasing core (7) and the second center core (8) so as to be longer than the length of read/write gap (3).
In the following, there will be described cases where the magnetic head of the preceding erasing type constructed as described above is used to record and regenerate data on and from a magnetic medium such as a floppy disk. First, there will be described the case where data is recorded on a recording medium. A signal corresponding to data to be recorded is applied to the input and output terminals (6a), (6b) of the read/write coil (6) while predetermined voltage is applied to the input and output terminals (12a), (12b) of the erasing coil (12). The erasing gap (9) slides on the recording surface of the recording medium preceding the read/write gap (3). Accordingly, as illustrated in FIG. 10, a predetermined current is allowed to flow through the erasing coil (12) and hence a predetermined magnetic flux is allowed to appear across the erasing gap (9) to erase the previous data (14) on the recording medium. Additionally, a current flowing through the read/write coil (6) based on the signal causes a magnetic flux to appear across the read/write gap (3) to record new data of the recording medium on a portion where the previous data (14) has been erased by the erasing gap (9), and hereby the write data (15) having guard bands (16) on opposite ends of the new data on the same will be written.
Alternatively, when the write data (15) is regenerated (read out), as the magnetic head is forced to slide on the recording surface of the recording medium without driving a current through the erasing coil (12) as illustrated in FIG. 11, a magnetic flux change in response to the write data (15) appears across the read/write gap (3) to drive a current through the read/write coil (6). Hereby, regenerated output voltage in response to the write data (15) appears across the input and output terminals (6a), (6b) of the read/write coil (6) for regeneration.
Additionally, there is also disclosed a prior example 3 illustrated in FIGS. 12 and 13 as another version of the magnetic head of the preceding type. The prior example 3 is intended to be more miniaturized than the prior example 2 by elimination of the center separator (13). Additionally, the first and second center cores (2), (8) are united into a single center core (17) and the first and second back bars (5), (11) are united into a single back bar (18).
The above-described magnetic head is also operable in the same manner as in the prior example 2 illustrated in FIGS. 8 and 9 in the case where any data is recorded and regenerated on and from the magnetic medium.
Now, in the magnetic head of the prior example 1 illustrated in FIGS. 5 and 6, an offset may sometimes be produced between a write data (15) track and a read/write gap (3) on the basis of causes such as eccentricity and so on when the write data (15) on the recording medium is regenerated. More specifically, a displacement may be produced between the read/write gap (3) and the writedata (15) and between the erasing gap (9) and the write data (15) as illustrated in FIG. 14, to result in the an offset (19) that is an overlapped portion between the erasing gap (8) and the write data (15). With the existence of such an offset (19), a magnetic flux is changed across the erasing gap (9) upon regeneration due to the write data (15) at the portion of the offset (19), and is circulated along a magnetic circuit composed of the erasing core (7), the second center core (8), and the second back bar (11) and is allowed to appear on a magnetic circuit composed of the first center core (2) and the first back bar (5) as a leakage magnetic flux. Hereby, the magnetic flux intersects the read/write coil (6) as a crosstalk magnetic flux for electromagnetic conversion. Accordingly, regenerated output voltage appearing on the input and output terminals (6a), (6b) of the read/write coil (6) is deteriorated in its S/N ratio.
Additionally, also in the magnetic head of the preceding erasing type illustrated in FIGS. 2 and 3, the erasing gap (9) is allowed to slide on the write data (15) upon regeneration of the write data (15) of the recording medium ahead of the read/write gap (13) as illustrated in FIG. 11, so that a magnetic flux is changed upon regeneration across the erasing gap (9) due to the write data (15), and is circulated through the magnetic circuit composed of the erasing core (7), the second center core (8), and the second back bar (11) and is allowed to appear on the magnetic circuit composed of the read/write core (1), the first center core (2), and the first back bar (5) as a leakage magnetic flux. Hereby, the magnetic flux intersects the read/write coil (6) as a crosstalk magnetic flux for electromagnetic conversion. Accordingly, regenerated output voltage appearing on the input and output terminals (6a), (6b) of the read/write coil (6) is deteriorated in its S/N ratio. The deteriorations of the S/N ratios are increased in the order of the conventional examples 1, 2, and 3.
There is disclosed a technique to prevent the deterioration of an S/N ratio caused by such a crosstalk magnetic flux produced due to the erasing gap (9) in Japanese Patent Laid-Open No. 61-148617 for example. Referring to FIGS. 15 and 16, prior example 4 is illustrated which includes a magnetic head disclosed in the above publication. In the figure, numeral (20) designates a short-circuit ring wound around the erasing core (7) which is disposed so as to induce a magnetic field in the opposite direction to an AC magnetic field induced on the erasing core (7) owing to the offset (19) upon regeneration.
In the magnetic head arranged as such any data is likewise recorded on and regenerated from a recording medium similarly to the prior example 1 illustrated in FIGS. 5 and 6. Additionally, even though where is produced any magnetic flux change across the erasing gap (9) upon regeneration owing to the write data (15), the short-circuit ring (20) operates to cancel out the magnetic flux change and hence restrict generation of a magnetic field along the magnetic circuit composed of the erasing core (7), the second center core (8), and the second back bar (11). There is therefore reduced the leakage magnetic flux that appears along the magnetic circuit composed of the read/write core (1), the first center core (2), and the first back bar (5). Hereby, there is improved the S/N ratio of the regenerated output voltage appearing on the input and output terminals (6a), (6b) of the read/write coil (6).
Additionally, there is also disclosed a technique (not shown) in Japanese Patent Appication No. 61-194615 in which an additional core is provided to the erasing core or a transformation circuit is provided on the erasing coil.
There is further disclosed a technique to eliminate crosstalk produced along the read/write coil (6) due to resonance between inductance and stray capacity of the erasing coil (12) when a current to the erasing coil (12) as a factor of production of another type of the crosstalk is off in for example Japanese Utility Model Laid-Open No. 63-157802.
Referring to FIG. 17, there is illustrated a prior example 5 disclosed in the above reference. In the figure, numeral (21) designates a diode connected across the input/output terminals (12a), (12b) of the erasing coil (12) with its cathode connected to the input/output terminal (12a) to which a plus DC potential is applied and with its anode connected to the input/output terminal (12b) to which a minus DE potential (or ground) is applied.
In the magnetic head arranged as such, as data is recorded on and regenerated from the recording medium as in the same manner as the prior example 1. The diode (20) short-circuits a current which is to flow owing to electromagnetic energy stored on the erasing coil (12) when the current to the erasing coil (12) is off upon the completion of the recording, so that resource through stray capacitance is prevented without causing any crosstalk on the read/write coil (6).
Additionally, referring to FIG. 18, prior example 6 is illustrated, in which a resistor (22) is connected instead of the diode (21) and which exhibits the same effect as the prior example 5.
Further, Japanese Patent Application No. 60-93603 discloses another technique, although not shown, to deal with any noise which might be produced when the magnetic head has not been operated for recording and regeneration on and from the magnetic recording medium, in which a noise-induced magnetic field is prevented from being produced and hence any data already recorded is protected, by short-circuitting opposite ends of the head coil of the magnetic head.
However, in the magnetic head of the prior example 4 illustrated in FIGS. 15 and 16, although the short-circuit ring (20) was provided on the erasing core (7) to suppress the affection of crosstalk to the read/write coil (6), the crosstalk being caused by a change in a magnetic flux produced across the erasing gap (9) due to the write data (15), the technique complicated the magnetic head and hence increased the burden upon manufacture of the same because of the provision of the short-circuit ring (20) on the magnetic head itself.
Additionally, in the prior examples 5 and 6 described with reference to FIGS. 17 and 18, although they were satisfactory in suppressing crosstalk to the read/write coil (6) during the current-off to the erasing core (12), it regrettably failed to reduce crosstalk along the read/write coil (6) caused by a change in a magnetic flux produced across the erasing gap (9) upon regeneration of data recorded on a recording medium. Moreover, in the technique wherein the non-magnetic center separator was provided in the center core, although the erasing crosstalk caused by a magnetic flux detected by the erasing gap was reduced by the existence of the non-magnetic layer, regeneration efficiency of the read/write core was deteriorated corresponding to the provision of the non-magnetic layer in the center core, and hence the S/N ratio was lowered. Still more, pseudo-gap noise was caused by the existence of the non-magnetic layer itself to considerably lower the S/N ratio finally, and further the center core was complicated in its manufacture, resulting in lowered yield and correspondingly in the expensive cost of the manufacture.